CN106383324B - A kind of lithium ion battery life-span prediction method based on capacity attenuation mechanism decomposition analysis - Google Patents

Abstract

The invention discloses a lithium-ion battery life prediction method based on capacity decay mechanism decomposition analysis. The polar equilibrium potentials are subtracted, and then corrected by polarization to obtain the equilibrium potential equation; Step 2, based on the different attenuation mechanisms of lithium-ion batteries, establish a multi-decay mode decomposition model, and through short-term aging tests, establish the multi-attenuation of the lithium-ion battery to be tested. mode fitting formula and predicting the decay trend; Step 3: Substitute the prediction result of the multi-decay mode fitting formula into the equilibrium potential equation of the lithium-ion battery to be tested to predict the remaining capacity. The present invention is based on the different mechanisms of lithium ion battery capacity decay, and the life prediction method for decomposition analysis of different decay modes solves the problem of simple extrapolation based on experimental test data or simple attribution of lithium ion battery life decay to a single electrochemical mechanism. .

Description

A Lithium-ion Battery Life Prediction Method Based on Decomposition Analysis of Capacity Decay Mechanism

technical field

The invention belongs to the field of lithium ion battery life prediction, and relates to a lithium ion battery life prediction method based on capacity decay mechanism decomposition analysis.

Background technique

Lithium-ion batteries have the advantages of high operating voltage, high energy density, long cycle life, and low self-discharge. They have been widely used in portable electronic equipment, electric vehicles, new energy power generation and storage, and space fields.

Compared with other types of secondary batteries, lithium-ion batteries have better life characteristics, better storage performance at room temperature and cycle performance. The storage life of lithium-ion batteries at room temperature can reach 6 to 8 years, and the long storage life of lithium-ion batteries developed for long-term storage life characteristics can even reach 10 to 15 years. The requirement is not less than 5 years and 10 years respectively. In order to test the life of lithium-ion batteries, a reasonable life prediction must be carried out using model methods.

When lithium-ion batteries are used in different work scenarios, their operating conditions are very different. When the lithium-ion battery is used as a power source for electric vehicles or a new energy power generation and energy storage system, the working conditions are mainly charge-discharge cycles; when the lithium-ion battery is used as a backup power source for a communication base station or other types of backup power sources, it is in a long-term shelving or Floating charge state, with occasional charge-discharge cycles; when lithium-ion batteries are used as energy storage power sources for smart grid emergencies and energy storage power sources for high-orbit satellites, they are in a storage state for a long time. However, in some traditional application fields of primary batteries with long storage life such as lithium thionyl chloride batteries and activated zinc-silver batteries, such as combat readiness power supply for missiles, power supply for field disaster alarm devices, and emergency alarm power supply for vehicle accidents, lithium ion batteries are used as A rechargeable secondary battery has the advantages of being repairable and having a long service life, and can replace the application of a primary battery. Under different operating conditions of lithium-ion batteries, the internal mechanisms leading to capacity fading are not exactly the same. The commonly used simple extrapolation, or the life prediction method that simply attributes the mechanism of lithium-ion battery capacity fading to the thickening reaction of the negative electrode SEI, cannot make accurate long-term predictions due to the lack of the mechanism basis of battery capacity fading.

SUMMARY OF THE INVENTION

The purpose of the present invention is to establish a method that can accurately predict the remaining capacity of lithium ion batteries in order to solve the problem of disconnection from the decay mechanism in the process of predicting the remaining capacity of lithium ion batteries.

In order to achieve the above purpose, the present invention proposes a lithium-ion battery life prediction method based on the decomposition analysis of the capacity decay mechanism, which includes the following steps:

Step 1. Based on the working principle of the lithium-ion battery, combined with the test data of the lithium-ion battery, establish the equilibrium positioning equation of the lithium-ion battery to be tested;

Step 2: Establish a multi-decay mode decomposition model based on different attenuation mechanisms of the lithium-ion battery, and through a short-term aging test, establish a multi-decay mode fitting formula for the lithium-ion battery to be tested and predict the attenuation trend;

Step 3: Substitute the prediction result of the multi-decay mode fitting formula into the equilibrium potential equation of the lithium-ion battery to be tested to predict the remaining capacity.

The method for predicting the life of a lithium ion battery based on the decomposition analysis of the capacity decay mechanism described in the above step 1 is characterized in that the equilibrium potential equation of the lithium ion battery to be tested described in the step 1, once the material system of the lithium ion battery is determined, the lithium ion battery is determined. There are four internal parameters of the equilibrium potential characteristic of the ion cell, or physical quantities that can represent these four parameters.

The internal parameters of the above-mentioned electrochemical model of the lithium-ion battery to be tested are the negative electrode active material content (Q _n ), the positive electrode active material content (Q _p ), the initial lithium intercalation amount of the negative electrode (y _s,n,0 ), and the positive electrode lithium intercalation amount ( y _s,p,0 ), or other physical quantities that can represent these 4 parameters.

The lithium-ion battery test data described in the above step 1 includes a button battery with the positive pole piece as the positive pole and the lithium piece as the counter pole, and the battery positive and negative poles of the button battery with the negative pole piece as the positive pole and the lithium piece as the counter pole. Equilibrium Potential Test. The test method is to charge and discharge the button battery at 0.04~0.01C.

The equilibrium potential equation of the lithium ion battery to be tested described in the above step 1 is obtained by subtracting the positive electrode equilibrium potential and the negative electrode curve equilibrium potential of the lithium ion battery, and adding polarization correction.

There are three multi-decay mode decomposition models described in the second step above, including active material decay, lithium loss, and capacity loss caused by lithium migration.

The short-term aging test described in the above step 2 is a short-term test according to the application environment. For example, in the normal temperature storage environment, the test time is 6 to 12 months, and the time nodes of the test data are ≥4.

In the multi-decay mode decomposition model described in the above step 2, the decay of the active material conforms to the kinetic law of chemical reaction, the loss of lithium conforms to the kinetic law of diffusion control, and the migration of lithium conforms to the linear law.

In the research on the life attenuation mechanism of various lithium-ion batteries, the reasons for the capacity attenuation of lithium-ion batteries are generally summarized as deactivation and degradation of active materials, decomposition and film formation of electrolytes, similar conductive agents and binders, and current collectors, etc. The degradation and decomposition of some electrode auxiliary substances, for batteries in storage conditions, also include partial electronic conductivity due to the presence of electrolytes, and leakage current caused by internal short circuits.

The invention is characterized in that the capacity decay of the lithium ion battery is decomposed into three independent factors according to different physical and chemical reaction mechanisms, and the internal basic working process model of the lithium ion battery is combined to extrapolate the law of the composite mechanism respectively. The capacity decay of lithium-ion batteries after storage is decomposed into 3 decay modes based on different chemical and physical mechanisms, and the different decay modes are described in accordance with their chemical or physical laws. The capacity decay of lithium-ion batteries is a combination of the three modes. the result of.

The method provided by the invention effectively shortens the test time, reduces the number of test samples, and improves the accuracy of life prediction.

Description of drawings

FIG. 1 is a flow chart of a prediction method based on different mechanisms of lithium-ion battery storage capacity fading according to the present invention.

Figure 2 shows the equilibrium potential curves of the positive and negative electrode sheets of the lithium-ion battery/lithium half-cell and full-cell.

Figure 3 is a prediction curve of the change trend of the decay rate of the positive active material of the lithium ion battery with the storage time.

Figure 4 is a prediction curve of the change trend of lithium loss rate of lithium ion battery with storage time.

Figure 5 is a prediction curve of the change trend of lithium mobility of lithium ion battery with storage time.

Figure 6 is a prediction curve of the change trend of the remaining capacity of the lithium-ion battery with the storage time.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings through specific embodiments. These embodiments are only used to illustrate the present invention, and are not intended to limit the protection scope of the present invention.

The lithium ion battery life prediction method based on the decomposition analysis of the capacity decay mechanism of the present invention decomposes the capacity decay of the lithium ion battery into three decay modes based on different chemical and physical mechanisms, and conducts different decay modes according to its chemical or physical mechanism. Regular extrapolation, the capacity decay of lithium-ion batteries is the result of the combined action of the three modes. As shown in Figure 1, the implementation steps of this prediction are as follows:

Step 1 (S1), based on the working principle of the lithium ion battery (that is, the basic electrochemical model of the lithium ion battery, which is a basic electrochemical model of Newman, which reflects the basic working principle of the battery, and the model is very complicated. A lot of simplifications), combined with the test data of the lithium-ion battery, establish the equilibrium potential equation of the lithium-ion battery to be tested.

Step 2 (S2): Establish a multi-decay mode decomposition model based on different attenuation mechanisms of the lithium-ion battery, and establish a multi-decay mode fitting formula of the lithium-ion battery to be tested through a short-term test and internal parameter analysis, and conduct the attenuation trend. predict.

Step 3 (S3): Substitute the prediction result of the multi-decay mode fitting formula into the equilibrium potential equation of the lithium-ion battery to be tested to predict the remaining capacity of long-term normal temperature storage.

The balance potential equation of the lithium ion battery is obtained by subtracting the positive and negative balance potentials and adding polarization correction. As shown in Figure 2, it is the equilibrium potential curve of the positive and negative electrode sheets of the lithium ion battery/lithium half-cell.

Among them, the equation of the positive and negative balance potential curve is:

E _s,p =-56.22*tanh((y _s,p -0.815)/0.06444-0.6047)+3900-50.64+72.31*tanh((y _s,p -0.9161)/(-0.04671)+0.04414)-70 +0.1639-6.826*tanh((y _s,p -0.8785)/0.01175+0.07663)+0.3165+5.886*tanh((y _s,p -0.9048)/0.01208-0.7693)+4+1.727+4.662*tanh(( y _s,p -0.8230)/0.02123-0.7281)-5+0.6463+2.835e+04*exp(-((y _s,p -0.4964)/0.09109).^2)-2.795e+04*exp(- ((y _s,p -0.4968)/0.09055).^2)+28.83*exp(-((y _s,p -0.6576)/0.05496).^2)-43.34*tanh((y _s,p -0.9547 )/0.01582-0.9212)-25-18.27-(1162*exp(-((y _s,p -1.003)/0.00578).^2)+10.7*exp(-((y _s,p -0.9951)/0.004413 ).^2)+332.1*exp(-((y _s,p -0.9888)/0.007013).^2))-(-44.69*tanh((y-0.9954)/0.003405-0.09323)-40-3.341) +1.385*tanh((y _s,p -0.6455)/0.01416-1.641)+2.5*tanh((y _s,p -0.6024)/0.01906)-2.5+8.969e+14*exp((-66.48)*y _s,p )+1884*exp((-12.91)*y _s,p ) (1)

E _s,n =-18.39*tanh((y _s,n -0.5)/0.03735)+108+0.6515-44.54*tanh((y _s,n -0.15-0.006406)/0.05096)+45-3.403*tanh( (y _s,n -0.1275)/0.004893)+2.5-1.835-2.286*tanh((y _s,n -0.325)/0.06918+0.3734)+3.5-3.139*tanh((y _s,n -0.4975)/0.004653 -0.3946)+1.529-2.157*tanh((y _s,n -0.675)/0.1274+0.04)+2.5+4.803*tanh((y _s,n -0.5)/0.03962)-4.387-1.041*tanh((y s,n -0.5)/0.03962) _s,n -0.21)/-0.005919)-1.113-2.585*tanh((y _s,n -0.175+0.005759)/(-0.005899))-2.569+1.428*tanh((y _s,n -0.1+0.01) /0.01129)+0.04329+2.138e+13*exp(-((y _s,n +0.04509)/0.00985).^2)+759.6*exp(-((y _s,n +0.02127)/0.03443).^ 2)+(-1.414e-15)*exp(39.1*y _s,n )-1.51-1*tanh((y _s,n -0.82)/0.03058-0.7512)-0.6-0.4102-0.8*tanh((( y _s,n -0.1507)/0.003407)+0.8-9.598*tanh((y _s,n x-0.0376)/0.006156-0.2812)-1.747+4.344*tanh((y _s,n -0.9385)/0.02503-0.1478 )+20-4.32-6.022*tanh((y _s,n x-0.05226)/(-0.008804)+0.06902)-6+7.936*tanh((y _s,n -0.02122)/0.004508)-8 (2)

The cell balance potential equation is:

or

E _ideal =E _s,p (y _s,p,0 +Dy _s,p ·(1-soc))-E _s,n (y _s,n,0 -Dy _s,n ·(1-soc)) +a (4)

Among them, E _ideal is the battery terminal voltage during the discharge process; E _{s, p} is the balance potential of the positive electrode; E _{s, n} is the balance position of the negative electrode; y _{s, p} is the amount of lithium intercalation of the positive electrode; y _{s, n} is the amount of lithium intercalation of the negative electrode ; y _s,p,0 is the initial lithium insertion amount of the positive electrode, y _s,n,0 is the initial lithium insertion amount of the negative electrode, is the discharge power obtained by integrating the ampere hour; Q _p is the capacity of the positive active material, Q _n is the capacity of the negative active material, Dy _{s, p} is the variation interval of the amount of lithium intercalation of the positive electrode, and Dy _{s, n} is the variation interval of the amount of lithium intercalation of the negative electrode ; SOC is the state of charge of the battery during the discharge process (the state of charge refers to the percentage of current power/total capacity); Q _all is the power that the battery can release under certain operating conditions. Even if it is discharged at a very small rate, the terminal voltage of the battery will be affected by the impedance, and a is the correction amount of various impedance effects during the discharge process.

After knowing any set of parameters in Table 1 (calculated according to the balance potential curve of the positive and negative electrodes and the full battery), the terminal voltage of the full battery at any time can be simulated.

Table 1: Equilibrium Potential Equation Parameter Set for Li-Ion Batteries

serial number Equilibrium Potential Equation Parameter Group for Lithium Ion Batteries 1 y_s,p,0, y_s,n,0, Q_p, Q_n 2 y_s,p,0, y_ofs, Q_p, Q_n 3 y_s,n,0, y_ofs, Q_p, Q_n 4 Other parameter groups describing the capacity of positive and negative electrodes and the state of lithium intercalation

Among them, the positive and negative offsets y _ofs are defined in the following two ways:

The above-mentioned test method for the balance potential curve of the positive and negative electrodes of the lithium ion battery and the full battery is to perform a charge-discharge test on the coin cell at 0.04-0.01C.

Based on the different decay mechanisms of lithium-ion batteries, a multi-decay mode decomposition model under normal temperature storage conditions is established.

(1) Attenuation of active materials: including changes in the amount of positive active material Q _p and the amount of negative active material Q _n ;

(2) Attenuation of active lithium: The total amount of active lithium in the battery can be defined as Q _Li =y _s,p,0 ·Q _p +y _s,n,0 ·Q _n , the attenuation of active lithium is the change of Q _Li ;

(3) Attenuation of lithium transfer: Assuming that the amount of lithium intercalation in the positive electrode does not change with the attenuation of the active material and active lithium, the lithium transfer can be defined as Q _Z =y _s,p,0,old ·Q _p,old -y _{s, p,0,new} ·Q _p,old , where new represents the initial state of the battery, and old represents the decayed battery state, so the decay of lithium transfer is the change in Q _Z.

Lithium-ion battery aging test

After the 18650 lithium-ion battery to be tested is fully charged, it is discharged to the cut-off potential at 0.04C, then charged to 4.1V, placed at room temperature, and stored for 12 months. C discharges to the cut-off potential.

Establish a decay model for the lithium-ion battery to be tested

The 0.04C discharge curve of the battery after storage is fitted by the basic working process equation of the lithium-ion battery to be tested, and the decay rate data of the three decay modes are shown in Table 2.

Table 2 The decay rate data of the three decay modes calculated based on the normal temperature storage test

Storage time (months) Q_p decay rate Q_n decay rate Q_Li decay rate Q_Z decay rate 1.0 0.007804 0.0003 0.006456 0.000873 2.0 0.01442 0.002798 0.01305 0.001836 2.9 0.02191 0.0015 0.01681 0.002846 3.9 0.02483 0.002109 0.02225 0.003983 4.8 0.03091 0.002341 0.02515 0.005184 5.8 0.03215 0.0022 0.0285 0.006404 6.8 0.0345 0.0005676 0.03122 0.00787 7.7 0.0542 0.002341 0.03343 0.009534 8.9 0.03841 0.002998 0.03789 0.01074 10.2 0.04343 0.002709 0.04169 0.0117 10.9 0.0439 0.003241 0.04255 0.0131 11.7 0.04368 0.003 0.04495 0.01413

(1) The decay of positive and negative active materials conforms to the law of chemical kinetics. The decay rate formula of positive and negative active materials is:

Where Q _p,0 is the initial heat release amount of the active material, Q _p is the amount of active material, t is the aging time, and A, B, C, and D are constants.

Combined with the test data of the lithium-ion battery to be tested, the formula for the decay rate of the positive active material of the lithium-ion battery to be tested is as follows:

f _Qp (t)=0.0765-(0.1559 t+27.1663) ^-0.7763 (8)

The variation trend of the decay rate of the positive active material with time is shown in Fig. 3. The test values show that the decay rate of the negative active material remains in the order of ^10-3 , which is ignored in the prediction estimation.

(2) The decay of active lithium conforms to the kinetic law of diffusion control, and the decay rate formula of active lithium is:

Among them, Q _Li,0 is the initial active lithium amount, Q _Li is the active lithium amount, t is the aging time, and D, E, F, and G are constants.

Fitting is performed in combination with the test data of the lithium-ion battery to be tested, and the formula for the decay rate of the active lithium of the lithium-ion battery to be tested is as follows:

f _Li (t)=0.0035·(0.7874·t+23.1987) ^0.5 -0.0170 (10)

The variation trend of active lithium decay rate with storage time is shown in Fig. 4.

(3) Lithium mobility and storage time conform to a linear law, and the lithium mobility formula is:

Among them, Q _Li,0 is the initial active lithium amount, Q _Li is the active lithium content, t is the aging time, and H and J are constants.

Combined with the test data of the lithium-ion battery to be tested, the lithium mobility formula of the lithium-ion battery to be tested is as follows:

f _ZY (t) = 3.9937 · 10 ^-5 · t - 4.9902 · 10 ^-4 (12)

The variation law of lithium mobility with storage time is shown in Figure 5.

Through the above three decay fitting formulas, the internal characteristic parameters of the battery after any storage time are estimated, and the prediction results of the internal characteristic parameters of the lithium-ion battery after long-term normal temperature storage are shown in Table 3.

Table 3 Predicted values of internal parameters of long-term normal temperature storage batteries

The above-mentioned internal characteristic parameters of the lithium-ion battery are put into formula (3) or (4), and the remaining capacity value after long-term normal temperature storage can be obtained, as shown in Figure 6. When the remaining capacity of the lithium-ion battery is reduced to 60-80% of the initial capacity, it is regarded as the end of life, and the specific standard is based on the regulations of the battery manufacturer.

To sum up, the present invention decomposes the capacity attenuation of lithium-ion batteries into three independent and interactive factors according to different physical and chemical reaction mechanisms, and combines the basic working process model inside the lithium-ion battery to carry out the corresponding mechanisms respectively. By extrapolation, the combined effect finally affects the capacity attenuation of lithium-ion batteries. This method can effectively shorten the test time, reduce the number of test samples, and improve the life prediction accuracy.

While the content of the present invention has been described in detail by way of the above preferred embodiments, it should be appreciated that the above description should not be construed as limiting the present invention. Various modifications and alternatives to the present invention will be apparent to those skilled in the art upon reading the foregoing. Accordingly, the scope of protection of the present invention should be defined by the appended claims.

Claims (7)

1. A lithium-ion battery life prediction method based on capacity decay mechanism decomposition analysis, characterized in that the method comprises the steps: Step 1: Establish the equilibrium potential equation of the lithium-ion battery to be tested in combination with the test data of the lithium-ion battery to be tested; Step 2: Establish a multi-decay mode decomposition model based on different attenuation mechanisms of the lithium-ion battery, and analyze the internal parameters through a short-term aging test, establish a multi-decay mode fitting formula for the lithium-ion battery, and predict the attenuation trend; The multi-decay mode decomposition model includes three decay modes: active material decay, active lithium decay, and lithium transfer decay; the active material decay includes changes in the amount of positive active material Q _p and the amount of negative active material Q _n ; The attenuation of active lithium refers to the change of the total amount of active lithium in the battery Q _Li , where Q _Li =y _s,p,0 ·Q _p +y _s,n,0 ·Q _n ; the attenuation of lithium transfer refers to The change of Q _Z , assuming that the amount of lithium intercalation in the positive electrode does not change with the decay of active material and active lithium, the lithium transfer is defined as Q _Z =y _s,p,0,old ·Q _p,old -y _{s,p,0, new} ·Q _p,old ; Lithium mobility and storage time conform to a linear law; The multi-decay mode fitting formula includes: the decay rate formula of the positive and negative electrode active materials, the decay rate formula of active lithium, and the capacity decay rate formula caused by lithium migration, wherein the decay rate of the positive and negative electrode active materials The formula is: where Q _p,0 is the initial amount of active material, Q _p is the amount of active material, t is the aging time, and A, B, C, and D are constants; The decay rate formula of the active lithium is: where Q _Li,0 is the initial active lithium amount, Q _Li is the active lithium amount, t is the aging time, and D, E, F, and G are constants; The calculation formula of the lithium mobility is: where Q _Li,0 is the initial active lithium amount, Q _Li is the active lithium content, t is the aging time, and H and J are constants; Step 3: Substitute the prediction result of the above-mentioned multi-decay mode fitting formula into the equilibrium potential equation of the lithium-ion battery to be tested to predict the remaining capacity. 2. the lithium ion battery life prediction method based on capacity decay mechanism decomposition analysis as claimed in claim 1, is characterized in that, in step 1, the equilibrium potential equation of lithium ion battery to be measured is subtracted by positive and negative electrode equilibrium potentials, After polarization correction. 3. the lithium ion battery life prediction method based on capacity decay mechanism decomposition analysis as claimed in claim 2, is characterized in that, in step 1, the equilibrium potential equation of lithium ion battery to be measured is: or E _ideal =E _s,p (y _s,p,0 +Dy _s,p ·(1-soc))-E _s,n (y _s,n,0 -Dy _s,n ·(1-soc)) +a Among them, E _ideal is the terminal voltage of the battery during the discharge process; E _{s, p} is the balance potential of the positive electrode; E _{s, n} is the balance position of the negative electrode; y _{s, p} is the amount of lithium intercalation of the positive electrode; y _{s, n} is the lithium intercalation of the negative electrode y _{s, p, 0} is the initial lithium insertion amount of the positive electrode, y _{s, n, 0} is the initial lithium insertion amount of the negative electrode, and t is the charging or discharging time; is the discharge power obtained by integrating the ampere hour; Q _p is the capacity of the positive active material, Q _n is the capacity of the negative active material, Dy _{s, p} is the variation interval of the amount of lithium intercalation of the positive electrode, and Dy _{s, n} is the variation interval of the amount of lithium intercalation of the negative electrode ; soc is the state of charge of the battery during the discharge process; Q _all is the amount of electricity that the battery can release under certain working conditions; a is the correction amount of various impedance effects during the discharge process. 4. the lithium ion battery life prediction method based on capacity decay mechanism decomposition analysis as claimed in claim 1, is characterized in that, the test data of the lithium ion battery to be tested described in step 1 refers to taking the positive pole piece as the positive pole and the lithium ion battery as the positive pole piece. The test results of the balance potential of the positive and negative electrodes of a button cell with the sheet as the counter electrode and the coin cell with the negative electrode sheet as the positive electrode and the lithium sheet as the counter electrode. 5. The lithium-ion battery life prediction method based on capacity decay mechanism decomposition analysis according to claim 1, characterized in that, the decay of the active material conforms to the kinetic law of chemical reaction, and the decay of the active lithium conforms to diffusion control kinetic laws. 6 . The lithium-ion battery life prediction method based on the decomposition analysis of the capacity decay mechanism according to claim 1 , wherein in step 2, the short-term aging test refers to a short-term test according to the application environment. 7 . 7. The lithium-ion battery life prediction method based on capacity decay mechanism decomposition analysis according to claim 1, wherein the short-term aging test comprises: for a normal temperature storage environment, the test time is 6-12 months, Among them, the time nodes of the test data are ≥4.